In the past, most composite ring structures have been manufactured using thermoset materials. When thermoset composite materials are used to produce a ring-type structure, the entire ring must be cured in an autoclave at a temperature that is suitable to bring the material to its final solidified state. During the autoclave process, the fibers within the thermoset material have a tendency to relax and lose alignment in the structure. The relaxation of these fibers is an undesirable event, since it is well known in the aft that fiber alignment significantly affects the strength and stiffness of a composite structure.
The processing of thermoplastic composite materials to form these types of ring structures, requires a very different type of machine and process than that utilized with thermoset materials. Several distinct advantages can be derived from the use of thermoplastic composite materials to produce structures such as cylindrical rings. Specifically, when compaction and consolidation of a thermoplastic composite material occur at the moment that the new material is added to the ring structure, as in a winding operation, the fibers in the matrix of the thermoplastic material are locked into whatever shape is given to those fibers at the moment of compaction and consolidation. As previously mentioned, locking the fibers in the matrix of a composite material into alignment significantly increases the strength and stiffness of the resulting composite structure.
However, most of the work that has been done in the area of manufacturing ring structures from thermoplastic materials, has focused on using convection heating to bring the thermoplastic materials to a temperature at which consolidation of the material can occur. Convection heating was introduced into the art of thermoplastic ring formation several years ago, to increase the speeds that can be achieved during ring formation. It was well known in the art that heat transfer through radiation and conduction could not introduce enough thermal energy into the thermoplastic material product to cause consolidation of the material at a rate faster than 1 to 2 inches per second. This type of rate refers to the speed at which new thermoplastic composite tape material is added to the old thermoplastic composite tape material in the ring structure being formed. Convection heat transfer is achieved by blowing hot gas onto the thermoplastic composite tape at the point where the new thermoplastic tape comes into contact with the old thermoplastic composite tape material of the winding ring structure being formed, causing melting of the material so that the new and old thermoplastic material combine into one solid mass.
Convection heat transfer, however, is undesirable in several respects, one of which being that it is extremely inefficient. Only a small proportion of the heat that is generated is actually used to heat the thermoplastic composite material. The majority of the generated heat blows about the vicinity of the impinging jets, heating the machine, bearings, spindles, and remaining structure. An additional disadvantage is that convection heating cannot heat the one place that it is intended to heat, the contact point of the new thermoplastic tape material that is being introduced with the old thermoplastic tape material in the wound ring, because the blowing gas stagnates at the acute angle between the introduced tape material and the wound ring. Stagnated convective heat has no velocity and therefore cannot transfer heat.
Additional problems are also encountered when winding a thick ring structure from thermoplastic composite materials. To form thick ring structures, larger amounts of thermoplastic material are required. This can be achieved by splicing several relatively short runs of thermoplastic tape material together. However, splices in the incoming material present discontinuities into the structure, thus lowering the mechanical properties of the product that is formed. Alternatively, a single extremely long run of thermoplastic tape material can be used to wind a thick ring structure, thus eliminating splices from the final product. The problem with this technique is that it is extremely expensive to have thermoplastic tape material manufactured which is several thousand feet long and that contains no splices. Several other cumbersome schemes have been contrived without success that attempted to splice material on the fly, or utilized a type of start and stop consolidation technique.
Thus, there is a continuing need in the art of thermoplastic ring formation, of a method and apparatus for winding ring structures (particularly thick ring structures) that is relatively inexpensive and can achieve high rates of manufacturing speed while utilizing conduction heat transfer to achieve consolidation of the thermoplastic material.